Electronic devices, such as semiconductor integrated circuits (ICs) or other semiconductor devices, are typically fabricated into and on a substrate, such as a silicon wafer, resulting in an IC area that must increase as the size and complexity of the IC increases. One trend in recent IC fabrication has been to increase the number and/or different types of ICs by vertically stacking and vertically interconnecting the ICs together. The vertically stacked ICs can be of different sizes, come from different size wafers, have different functions, be made of different materials, etc.
One method for realizing the approach of vertically stacking ICs is through a direct bond process in which vertical interconnect structures are bonded together between individually stacked ICs. This approach may be accomplished by using conventional wafer fabrication techniques, including wafer thinning, chemical-mechanical polishing, photolithography masking, via etching and deposition, and electrical interconnect and electrical trace deposition. The vertical electrical interconnection between stacked ICs can be formed as a result of the direct bond stacking, or as a result of a sequence of wafer fabrication techniques after direct bonded stacking.
A typical direct bond process provides an electronic device substrate, such as a semiconductor IC substrate, having a bonding layer and vertical interconnects extending through the bonding layer. The vertical interconnects are connected to electrical traces disposed on the substrate, which provide an electrical path to circuits or devices on the substrate. During the direct bond process, the bonding layer of one electronic device is contacted with the bonding layer of another electronic device, whereby a chemical bond may occur with or without temperature treatment. In addition, exposed portions of the vertical interconnects of the first electronic device are contacted with the vertical interconnects of the second electronic device to enable an electrical coupling between electronic devices in the vertically stacked electronic device assembly. Commonly, after the desired number of individual electronic devices have been vertically stacked, the stacked electronic device assembly undergoes a relatively high-temperature treatment to cause the vertical interconnects from each electronic device to be sufficiently diffusion bonded together.